Looking Back at Orion

byPaul GilsteronSeptember 23, 2006

Whenever I think about Project Orion, I recall the ‘putt-putt’ experiments that tested the propulsion concept back in 1959. It was hardly an atomic spaceship, but the little putt-putt called ‘Hot Rod’ is as far as Orion ever got operationally. Using chemical explosives, Hot Rod rose 100 meters, a brief flight that nonetheless validated the idea that a spacecraft built around nuclear bombs, propellant and a pusher plate could be made to take stable flight.

An atomic spaceship. There was a time when the idea seemed to have interstellar possibilities. Freeman Dyson, a key figure in Orion, envisioned one version that used a copper pusher plate twenty kilometers in diameter. Driving the ship would be a nuclear arsenal of staggering proportions: 30 million nuclear bombs, each of which would explode 120 kilometers behind the vehicle at intervals of 1,000 seconds.

With a total acceleration time of five hundred years—and a comparable time for deceleration—this mammoth super-Orion would carry a colony of 20,000 Earth people to Alpha Centauri. Flight time: 1,800 years, making it a true multi-generation ship, where the distant descendants of the initial crew arrive at the target to make a new start for humanity. Later Dyson would ponder a pared down version that used 300,000 bombs to reach a final velocity of 10,000 kilometers per second, with arrival at Alpha Centauri in 130 years.

These days Project Orion’s interstellar capabilities seem vastly over-rated, even though its potential for travel to the outer Solar System was very real. Dyson himself now considers nuclear options unviable for missions to another star. When I was researching my book, I asked him his current views about Orion as a way to reach Alpha Centauri. Here’s a bit of what he said:

The Orion idea was exciting, but as far as interstellar trips are concerned, nuclear energy just doesn’t cut it… Youre using less than one percent of the mass with any kind of nuclear reaction whether it’s fission or fusion. The velocities you get are limited to much less than a tenth of lightspeed. Nuclear methods are great inside the solar system but not outside; in interstellar terms, they are not very interesting.

But what a story, and if you haven’t read George Dyson’s book about his father’s work, you’re missing out on a great experience. It’s Project Orion: The True Story of the Atomic Spaceship (New York: Henry Holt & Co., 2002). Online, the ever-reliable Anthony Kendall offers up a fine account of Orion. Here Kendall describes the vehicle, which would have dwarfed any rocket ever made:

A full-size Orion vehicle would have had a mass of 4,000 tons – about 40 times that of the Space Shuttle – and would include a “pusher plate” about 1-meter thick at the center. This solid mass of metal served to reflect the Orion craft away from the nuclear explosions, while at the same time protecting the passengers from the neutron radiation. The enormous shock absorbers between the pusher plate and the crew module would then distribute the 10,000 G’s of each nuclear blast to something much more comfortable for Orion’s passengers. In fact, an Orion launch would probably be much more comfortable than a conventional chemical rocket because of the sheer mass of the vehicle.

So vast were some Orion concepts that Ted Taylor, a weapons designer who became a guiding force behind the project, once considered installing a 4000-lb barber’s chair on the ship, thumbing his nose at the piddling chemical rocket designs that measured out payload in teaspoons. But of course, those chemical payloads got larger even as political currents made the nuclear option less realistic. The nuclear test ban treaty was but one of many blows that put an end to the program. Dyson talks about all this in Disturbing the Universe (New York: Harper and Row, 1979).

Be sure to read Kendall’s account for the overview, then George Dyson’s book, a volume I could hardly put down. And if you want to follow some of the interstellar references, start with Freeman Dyson’s paper “Interstellar Transport,” in Physics Today (October, 1968), pp. 41-45. The drama of Orion’s demise is told in Dyson’s “Death of a Project: Research Is Stopped on a System of Space Propulsion Which Broke All the Rules of the Political Game,” Science 149, No. 3680 (July 9, 1965), p. 141. And keep an eye on an Orion descendant called External Pulsed Plasma Propulsion, which may have much to teach us still.

Comments on this entry are closed.

Eric JamesSeptember 24, 2006, 4:47

I remember reading some sci-fi bok where a bunch of guys in Bellingham Washington made such a vessel and used it to defeat an elephant-like alien invasion force. Funny that I’d remember the name of the town in the book, but not the name of the book or the author.

I did read an interesting article on Orion about a year ago or so (I think it was in Discover). Quite a concept.

I don’t think it’d be a good idea to use it from earth to orbit, but perhaps a lunar base launch might be practical? The materials to build it would be handy, you’d get a quicker start, and you’d not need to concern yourself quite so much with environmental considerations.

I especially like the heavy payload ability. This would come in particularly handy when equiping an outer-solar colonization effort. Heck, you could even use this technology to move massive asteroids and comets around.

Hmm within the last few years I remember reading of simulations using an Orion concept. The premise was extremely condensed magnetic fields compressing gram, or smaller, sized pellets of fissionionable and then channeling the exhaust. I can’t for the life of me remember more details but apparently there was nothing to forbid it and it was deemed achievable with current tech.

The prime points from this simulation were a huge reduction in mass (pusher plate was vastly reduced in size) and an exponential reduction in fissionables needed (due to vastly improved effeciency).

The mini-pulse design you describe is Andrews Aerospace’s Mini-Mag Orion, which is quite an interesting design from a safety point of view because there are no self-contained ‘bombs’ being used. Also the reaction is totally controlled, unlike the riskier approach used in a Nuclear Saltwater Rocket.

The gigantic design that Paul discusses is the ‘Power Limited’ version of an Orion starship in which all the excess thermal energy is radiated away. As the work on Orion indicated using an ablative pusher plate only results in a minor mass loss, so the giant copper dissipator isn’t really needed.

With a magnetic+solar sail for braking an Orion could double its reference speed of ~ 0.03 c. Robert Enzmann’s gigantic Orion based starships, which Rick Sternbach has painted so evocatively, had mass ratios of ~ 100 and could push towards ~0.1 c. There would need to be an incredible amount of refinement of fusion plasma bombs to reach that efficiency, and mining 12,000,000 tons of fusion fuel from a gas giant would be an immense undertaking.

Getting around a star system fusion pushers are pure ‘Flash Gordon’ in potential, but they’re really marginal for interstellar travel. Firing fuel pellets at a starship would be a neat hybrid of mass-beam/pulse drive, though getting them to fuse usefully will be a real trick. I think high-speed impact has been suggested and experimented with as a fusion trigger, but I’ve no idea of the efficiency.

What I found really interesting about the big Orion vehicles (that could lift) millions of tons. Is that they could be used to establish full size and self sustaining industrial operations in stable orbit (L5), on the moon and on Mars. Go through the Earth’s atmosphere once and then make more bombs on the moon and colonize the solar system. Only more people and some small difficult to make new technologies would need to be moved off the earth after that once big move.

The alternative is for new, safer and smaller systems to establish that solid beachhead on the moon and then to make some super heavy (million ton) and fast movers to get a lot of stuff to Mars and the asteroids.

Efforts and plans where we have to spend more than 0.1% of human GDP to go to the stars will not be realized. Therefore we first need to get exploiting in solar system resources and move up to Kardashev 1.3-1.7 and then we can more easily afford sending serious expeditions out to other star systems. A plan that breaks the bank for an Apollo style and go and do little is not worthwhile.

All the odd bits on the wave guide are for fine-tuning believe it or not. I’ve seen some very odd looking antenna horns and the like thanks to a radio technician I know, so don’t be too surprised. A few screws and bolts and odds and ends make for a finely tuned wave-guide.

Shawyer’s thruster will be a fun system for milligee trajectories, but needs awfully high power densities to get rocket-like thrust for all but slow speeds. What would really make it a space-drive would be if it gained power straight from zero-point fields, but that’s a whole different kind of resonant cavity.

The only propulsion system that I now consider feasible (in the foreseeable future) for interstellar spacecraft, or at least for small robot probes, is laser propulsion. That is, huge laser installations on the moon (powered by nuclear fusion) pushing a stellar probe’s laser sail. The huge advantage is that you won’t need any on board fuel, nor an engine, and that there is for that reason virtually no limit to speed (well, up to a considerable proportion of light speed). The only big disadvantage is that the probe won’t be able to slow down this way. So you will have to send out lots of small probes that will just race through another planetary system in hours or days (after a journey of many years). This is a feasible idea anyway, since by far the greatest part of the cost will be the laser installations and not the probes themselves. I consider this probably the first mode of interstellar exploration that mankind will do.

That clockwork doesn’t look like a tuning device. It looks more like a movement. I note that the gear reduction appears to come from the center shaft outward, therefore using an outer gear as a thumbwheel to tune it would probably not be conducive to “fine tuning”. Also, note all the extra screws and nuts in the flanges that don’t seem to fasten to anything. What are they for (other than to make it look unnecessarily complicated)?

Ronald,

That’ll never happen. It won’t happen for a lot of reasons. My favorite is that fusion reactors will probably never have sufficiently high, sustained Q to power much of anything. I think they got the physics wrong. An applied external compression force is just never going to be the equivalent of a steep gravitational gradient.

Eric, that picture looks all fixed to me, not like a clockwork. There has to be a fair amount of force holding the wave-guide together tightly too, especially at high Q factors.

As for fusion reactors, the gravity gradient of the Sun isn’t super-steep, and the reaction rate of fusion within stars is actually quite low, per unit volume of star-stuff. What makes the difference is the confinement volume is immense. A current tokamak creates fusion conditions in a very thin ring of plasma, so there’s no wonder it’s hard to maintain. But current research reactors can hit breakeven and ITER should easily get an order of magnitude more power.

What’s irritating about the whole effort, to me, is the glacial pace the fusion community believes it needs – ITER will be built c. 2016, then they want 15 years of playing with it, and the Fusion Materials Facility, so they can decide by 2031 whether they can build an actual power-reactor version, which should be completed by c. 2048!!! So they can then retire?

Fission went from test reactor in 1942, to power reactor in 1952 (I think) without all the apparent screwing around.

Ronald, to power lasers for interstellar travel in space what’ll be needed is self-replicating solar power satellite fabricators. In a few decades these could supply enough power to launch thousands of starships, not just probes, per year.

Probes are pointless because of the communication lag-time, because advanced space-based telescopes can do all the remote sensing of nearby exoplanets we could possibly want before sending actual survey teams. Fictionally lots of writers imagine we’ll sit on our backsides for decades/centuries waiting for results from slow-probes, but I just don’t buy it.

If manned vehicles are limited to low sub-cee then maybe fast probes will become a priority, but not without braking for extended observations. Laser probes can deccelerate using mag-sails incorporated into their sail structure, so this isn’t a real limitation. Mag-sails will also be useful for manned vehicles too.

Fusion confusion, infusion and more
Funding required, greenbacks for sure
Hydrogen heated with lasers that cook
Energy forever, if they get it to work

Consumption presumption, gumption and more
Heat from a source, like from the sun’s core
“It’s coming soon.” they assert once again
Here I am wondering, just when is then?

Conflagaration fiction, confliction and more
It passes from fact to myth then to lore
“Unlimited energy.” I hear them yet say
Just burn the money, it’ll cost less that way…

Laser fusion is an inoperable boondoggle… it won’t work because it can’t work.

Particle scientists everywhere have forgetton the basics. Conservation of momentum and conservation of energy will always prevent the system from putting out more practical energy than is input. The funniest part though is that it will always seem like they’re real close to a breakthrough because virtually all of the input energy is bounced back out!

“Look! It’s working near breakeven Sven!”

“Yah! Vit juzt a leetle more juize ve can make it verk!”

They’ve been saying things like that for over half a century now. The reactors get bigger, the results are always the same.

The tokamak systems seem to be following a similar pattern. What happened to that recent Chinese test? Anyone know the results?

The results AREN’T always the same. The energy return has systematically increased with every new round of experiments. They really are getting better at doing it BUT it’s still fiendishly expensive and ridiculously gargantuan machinery is created each time the field advances.

I disagree. If they really knew what they were doing they’d have had it operational soon after they first started saying they were close to being successful (like about 40 years ago!).

Although Q has consistently approached breakeven, It hasn’t blossomed into the overwhelming extra energy required to power the system plus a lightbulb or two (much less make up for the the already spent start-up energy).

Granted, I’ve seen reports of Q higher than 1. However one must ask if these higher Q numbers were the result of controlled fusion, or simply a brief runaway reaction? In either case, they aren’t significant in the “practical “sense.

hello all i enjoy reading about hypothetical means of spacecraft propulsion and enjoyed this group of comments.had an idea a bit ago after reading a book,i think the first one in which i encountered the “cosmic foam” or zpf.i said to myself,the energy that must exist just in the very stucture of space time itself!! if we could tap into it we could then have a spacecraft that would have an inexhautable supply of fuel which would be everywhere and which our ship would not have to carry.as to velocity? your guess would be as good as mine.when i first thought of this i figured it was “my idea” lol then i found out that “my idea” went back to about 1947,before i was born!! but still i have always liked the concept.you too?what does everybody think? respectfully george

this interesting discussion is going in diffreent directions, and there is some confusion:
Eric James: I was not talking about the particulars of laser fusion, I was talking about (any) nuclear fusion as a prerequisite for abundant energy, to fuel lasers. Probably the only possible (foreseeable) source of abundant energy needed for stellar travel will be fusion.
So, if and whenever (and however) mankind masters nuclear fusion, it will be possble to power laser installations powerful enough for propulsion of a small probe with light sail, be it still with low accelleration, sufficient to make it attain a reasonable proportion of c, by the time it reaches the edge of our solar system.
Adam: with due respect, your view seems overly optimistic: “self-replicating solar power satellite fabricators. In a few decades these could supply enough power to launch thousands of starships, not just probes, per year”.
I agree, however, with with the idea of laser-probes with mag-sails for braking. OK, so they won’t just zoom by, but actually break to hang around. Much better. With ever-increasing computer power, an (almost) Artificial Intelligence stellar robot-probe, that knows quite well what to do, will probably be feasible within decades (again, provided we manage to master sufficient energy). It seems likely that mankind will always first send probes than humans: smaller, cheaper, safer.
See Zubrin’s “Entering space” for more on this.

The problem with fusion, as a source of energy for use on Earth, is that it solves the wrong problems.

Fusion programs were initiated in the 1950s, when there was serious concern about the amount of uranium that could be mined. Fusion would use cheap and essentially inexhaustible deuterium and lithium. Fission breeder reactors were also motivated by this concern.

However, in the decades since then, uranium has turned out to be available in much larger quantities than had been anticipated. The Japanese have a technology for absorbing it from seawater on suspended polyamidoxime polymers that would provide billions of tons of the element at prices only a few times higher than the current spot market price.

Fission’s big problem has been the cost of building the reactors themselves, not the cost of the fuel. Fusion moves in the wrong direction here, since a DT fusion core of a given thermal power is projected to cost an order of magnitude more than a fission reactor of the same power.

Now, maybe you’ll say fusion solves the waste problem. But it doesn’t, really. The mass of activated material in a fusion reactor will be large. Fission fuel has the advantage of being more concentrated, if also much more radioactive. It can be sealed away in dry casks and allowed to cool for decades or centuries, so the net present value of the cost of ultimately getting rid of it can be made exponentially small (through the miracle of nonzero interest rates).

The fact that fusion programs are making such slow progress is a symptom of the marginal nature of the benefits expected from the programs. If it were such a huge win, you’d see everyone putting more effort into it.

Conservation of momentum and conservation of energy will always prevent the system from putting out more practical energy than is input.

The conservation laws say no such thing. Where are you getting this nonsense? Fusion may end up being impractical, but this isn’t because of some mystical effect of conservation laws, but because of mundane considerations of economics and engineering.

I disagree. The mere fact that it hasn’t been operable at any of the scales originally envisioned seemingly indicates that something is missing in the basic concept.

If it isn’t the conservation laws holding us back, what is it?

Your reasoning, such as it is, is bizarre in the extreme. We have known you can get positive energy payback from man-made fusion since the first H-bomb test. Are you claiming the conservation laws don’t apply on pacific islands? Or what about stars — are the conservation laws not working there either? Or are you claiming that neither H-bombs nor stars get their energy from nuclear fusion?

You are committing an elementary logic blunder, confusing “if something is prohibited by conservation laws, it won’t work”, with “if it won’t work, it’s prohibited by conservation laws”.

To answer your last question: the engineering is very difficult. Engineering can be difficult even on projects that don’t violate conservation laws.

Are you trying to say that the physics in a runaway fusion explosion is the same as the physics in a “controlled fusion” reactor?

They’re in the same universe. The same laws of physics apply. If conservation laws made controlled fusion impossible, they’d make ‘uncontrolled’ fusion impossible also. After all, the conservation laws don’t have an ‘except in what Eric James calls “uncontrolled”‘ exception to them.

You didn’t ask for the basis of my reasoning before you condemned it, so I thought I should leave this here for posterity.

“Why Laser Containment Doesn’t Work”

The basic premise of hot fusion is that you suspend a bit of “fuel” in the crossfire of a bunch of bazillion watt lasers. The momentum of the laser photons is supposed to contain and compress the fuel while the kinetic energy is supposed to heat the fuel. Viola! The fuel reaches the correct pressure and temperature to begin fusing. However this method hasn’t been able to sustain fusion and create enough energy to equal the input, much less have enough left over to power a lightbulb. Why?

The fault in the premise is two-pronged, mostly having to do with those pesky laws of motion and conservation that physics classes gloss over too quickly these days.

First, let’s examine “inertial containment.” This is the use of the photon’s inherent momentum to apply force to the fuel to compress it. This sounds plausible (and it sort of works), but does it work as anticipated? No. Why?

The laws of motion state that for every action there is an equal and opposite reaction. Basically, by pushing on the fuel, the fuel reacts by pushing back. Since its “back” is against the “wall” of another laser beam pushing on the other side, all of the momentum applied to the fuel to compress it must be realized as an equal and opposite push outward of the fuel to resist compression. Basically, you can suspend the fuel and compress it to a degree, but you can’t compress it indefinately. Eventually you reach a limit of compression wherein the fuel is pushing back Just as hard as the lasers are pushing in. Essentially, it becomes a perfect reflector.

Momentum isn’t the only story though. Containment must always be lost. Why? Because of the kinetic energy (not to be confused with momentum). Tremendous amounts of kinetic energy. A bazillion watts in the space of the fuel pellet.

As the fuel absorbs energy from the lasers, the photons are converted into kinetic energy within the fuel. Kinetic energy that compounds the effects of, and works in parallel with the forces of momentum trying to push the fuel’s boundaries outward from the center.

In other words, the more energy you apply, the more energy you need for containment, so the more energy you apply, so the more energy you need for containment! It’s a vicious cycle! Eventually, containment must be lost.

The energy levels of the fuel do rise to a point where fusion is obtained (reportedly), but it doesn’t seem likely that the energy input to output will likely ever rise to utilitarian levels using this method.

The sun works because the pressure of gravity is not an externally applied inertial force. It’s merely a compression from an internal force. The compression is suspended by the intense kinetic energy put out by the fusing mass, but it’s a war of force that the fusion mass must eventually lose. Someday, the sun will likely explode and then collapse into a white dwarf. Basically, the mass of the sun “wants” to inhabit a smaller space. Only the kinetic energy of fusion is preventing a collapse. The forces are currently in balance. The sun maintains its form.

Earthbound fusion is just the opposite. The war of energy and momentum between the lasers and the fusing fuel must be lost by the lasers. When this happens, containment is lost. Basically the mass of earthbound fusion “wants” to inhabit a larger space. Additionally, as in the solar example above, the kinetic energy of fusion enables expansion. Therefore there is no balance of force, but rather a linear expansion. The combined forces of momentum and KE need simply to exceed the forces of the inertial containment in any given moment. Since KE is continuosly added (unlike with the sun), the expansion forces must always eventually accumulate to a point where they exceed the laser’s inertial confinement force.

Another way of looking at it is to consider explosive force. The lasers compress the fuel to the point of fusion and the fuel is super-energized by the fusion process. Suddenly, the lasers are pitifully weak in comparison to the burst of energy put out by the fusing mass. The fuel suddenly expands. Coincidently, the force of the lasers decreases by the square of the distance from the focal point. Therefore the more the plasma expands, the easier expanding becomes.

So ironically… the quicker containment is lost, the more successful the fusion process was to begin with!

If substantially more than breakeven is not achieved, then it’s more practical to apply the energy directly to the propellant than to a mid-stage, power consuming fusion process. The problem though is that the energy required to sustain the fusion and apply energy to the propellant is supposed to come from the fusion process. In other words, without pacticable fusion there isn’t enough energy available to energize the propellant fo the long duration, interstellar flight would require. Therefore you don’t have a deep-space drive. It’d only be good for local use (simply, a regular ion drive)..

Finally, an unusual aircraft exhaust contrail photographed in
Ohio last month suggests that experimental research into “pulsed
detonation engines” or other forms of exotic propulsion
continues. The distinctive “donuts on a rope” contrail was
photographed east of Dayton, Ohio on November 10, 2006 by
William D. Telzerow. See:

My personal gut feeling is that the Orion Project was shot down when they realized the industyr that would spring up around it. Imagine in today’s world an industry that consumes mini-nukes for spacecraft propulsion. How long do you think that would last? My guess is less than a second. It would only ever be an idea. The possibility that a nuke or thermonuclear pellet gets into the hands of a rogue regime or terrorist group is simply too great to ignore.

The use of nuclear weapons was a foregone conclusion by in World War II. Project Orion ‘should’ have been implemented before the Soviets tested their first bomb.! Could you imagine what are world would look like now? Though I suspect Stalin & Khrushchev would have been ‘convinced’ that permanent occupation in space & other planets would be necessary for ‘peaceful’ co-existence. I’d doubt the atmospheric testing issues would have occurred, if millions of people were space traveling by 1955?I smile at the idea of landing on the Moon or Mars before the first atomic submarine was built.
I wonder what my ‘doppelganger’ in that alternative 2013 would be doing now? Would I be living around Jupiter, Saturn or arriving in Alpha Centauri enjoying my retirement?

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last twelve years, this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

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